Royal Evo going FASST

I have managed to attach the Futaba T6EXP 2.4 GHz transmitter to the buddy connector of my Multiplex Royal Evo 12. It transmits seven channels.

I am not recommending this modification to anybody. I am only reporting what I did and how. I will not write a detailed how-to, because I think that only people with sufficient skills in electronics should try the experiment at this time. If you wish to do so you do it at your own risk.

First, the receiver: I have added the small 220R resistor, which is missing at the 7th channel's signal lead. By looking at the pic the above link points to you will easily find out where the resistor is missing. After that, my scope displayed a servo signal in neutral position (1.5 ms) at the lead.

Second, the transmitter: It sits piggy-packed on a somewhat larger board, which carries the LEDs, the buddy connector, and the 5V voltage regulator. If you open the case and look at this board, you will see four leads connected on the left and three leads on the right side of the board. The four leads on the left are for the buddy connector only, so I removed them. The three leads on the right carry ground, battery plus, and the signal. The signal package is a usual 22 ms frame with the servo pulses active low and 3.3V peak voltage.

Third, adapting the Evo's buddy connector: Pin 4 carries the servo signal package, active high, the peak voltage is the same as the battery voltage. I made a small inverter circuit, using a BC547, a 4k7 resistor at the collector lead, a 3V3 Zener diode between collector and ground, and a 10k resistor at the base lead. I connected the inverter to the regulated 5V on the larger board.

The supply voltage comes from pin 2 of the buddy connector. Pin 3 is connected to battery minus or ground. You have to bridge pins 5 and 3 in order to switch the Evo's Hf transmitter off and have the signal routed to pin 4.

That's all. The 2.4 GHz box is working flawlessly and fully transparent as the Evo's transmitter modul.

I am also reporting my experience as a criticism to Futaba:

Why was the R606FS artificially limited to six channels?
Why do you let us wait for a 7-channel 2.4 GHz solution which fits the needs of advanced model pilots?
Why couldn't you do what I did as a product? A 2.4 GHz 7-channel modul that can be attached to the buddy connector of almost any radio would be welcomed by many model pilots.

Here is the adapter circuit that has been checked against a number of Transmitters (i.e. Multiplex Royal Evo, 3030, 4000, Graupner MC-22). Input is the PPM data stream that is available at the buddy connector. Polarity does not matter. Supply voltage (7 ... 25V) can as well be drawn from the buddy connector and is passed through to the T6 Tx module, which has its own 5V-regulator.

The adapter forms a PPM data stream with positive pulse widths the Tx module can interpret. Different pulse widths switch the Tx module to different modes. These are the pulse widths and the respective modes as published by Rudy on the German RCLine board:

Since capacitor specs are usually not precise, you cannot rely on achieving the desired pulse widths with the computed R/C-values (12k, 1k2, 33n). So, instead of the 12k resistor I am using a 5k trimmer in line with a 10k resistor. With the switch open I adjust the trimmer so that the module switches to power down mode (green LED on, red LED blinking). Then, by closing the switch, it safely goes to regular transmission including failsafe.

Again, I am only reporting what I did. I am not recommending this mod to anybody. Because of the high risk a transmitter shut down could cause, the adapter circuit should be built and used only by people who have sufficient skills in building electronic devices.

Name it whatever you like, Ron. Fact is that it combines Futaba's 2.4ghz technology with all the comfort the Evo has to offer, apart from the 7 channels limitation. I have no need for more channels at this time. So I am quite satisfied.